1. Field of the Invention
The present invention relates to power tools such as impact wrenches and, particularly, to mechanisms for limiting the torque which such tools can deliver.
2. Description of the Prior Art
It is known to provide torque-limiting clutch mechanisms in various types of rotary devices, including rotary power tools, such as air impact wrenches. Many such prior art slip or torque-limiting clutch mechanisms are constituted by rigid metal bodies, such as steel balls, which are disposed in radially directed grooves and are displaceable between an engaged condition and a release condition. They are retained in their engaged conditions by an elastic force generated by pressure springs which act directly, or via hydraulic plungers. Consequently, such clutches are relatively complicated from the structural point of view and are not suitable for use in impact tools. Furthermore, many such slip clutch arrangements are not readily adjustable for varying the torque at which the clutch will slip.
It is also known to provide a radial torque limiting mechanism which includes resilient rods or arms having fingers engageable in corresponding radial slots or recesses in a driven member with a force with is variable. When the load torque exceeds this force the arms slip out of the recesses and rotate relative to the driven member. Such arrangements have not heretofore been used in power tools.
Other types of torque-limiting coupling devices have utilized flat cam surfaces disposed in camming engagement with polygonal cam follower surfaces, but such arrangements have not been adjustable for varying the torque at which the mechanism will slip.